Mike Harris, an undrafted rookie from UCLA, will start at left tackle Monday for the Chargers. It's a demanding assignment for a player who usually played right tackle for the Bruins.

San Diego Chargers rookie tackle Mike Harris has made a habit out of defying… (Gregory Bull / Associated…)

As an offensive tackle at UCLA, Mike Harris had the unusual distinction of being named the Bruins' most improved offensive player two years in a row.

But no such award could adequately capture the leap he has made since August.

Harris, an undrafted rookie, will start at left tackle for the San Diego Chargers when they open the season Monday night at Oakland. That's right, a guy who didn't even hear his name read on draft weekend will now be protecting the blind side of Pro Bowl quarterback Philip Rivers.

That's a career leap that can't be quantified by a tape measure.

"It's really amazing," Harris said by phone Thursday. "It's a dream come true. I've worked my whole life to get to where I want to be, and now my teammates and coaches are counting on me."

Harris was moved into the starting lineup in place of Jared Gaither, who wants to be fully recovered from back spasms before he comes back. There's no timetable for Gaither's return.

Left tackle has been a problem spot for the Chargers for some time. Tackle Marcus McNeill suffered a season-ending neck injury in a home loss to the Raiders last November and was briefly replaced by Brandyn Dombrowski, who was overwhelmed by pass rushers in that game. The Raiders had six sacks, four by linebacker Kamerion Wimbley, who is no longer with the team.

That prompted the signing of Gaither, who stabilized the position at the end of the season.

Now, with Gaither and Dombrowski hurt, and McNeill retired, the Chargers have turned to Harris, saddling him with quite a responsibility, left tackle generally considered the most difficult position on the line.

Asked about his confidence in the rookie, Rivers told reporters: "It's high. There's no reason for it not to be. … It's not as if he just showed up here today and said, 'Hey, I'll be ready to go.' The group we've practiced with the last month is the group that's going to play Monday night."

Rivers is coming off his toughest season, and breakdowns in protection played a role. He had 25 turnovers, including five fumbles and a career-high 20 interceptions.

The Harris experiment is risky. Despite his prototypical size (6 feet 5, 310 pounds), he was not a bright blip on the radar of pro scouts and was mostly a right tackle in college, although he spent time on both sides in the "pistol" offense during his last year.

"I can't really tell you why I wasn't picked," Harris said. "I felt like I should have been drafted, but I'm just going to play with a chip on my shoulder. I know that 31 other teams missed out on a hardworking, great offensive lineman. But I'm not going to hold my head down on that."

In the Southern California region, USC tackles Tyron Smith and Matt Kalil got all the attention. Smith was drafted ninth by Dallas in 2011, and Kalil was taken fourth by Minnesota in April. Both are starting for their respective teams.

Said Harris: "Starting Monday, I'm going to have a chance to show the world who Michael Harris is, and show the world I belong in the NFL."

Already, he's notched one victory. His father was a die-hard Raiders fan who now roots for the Chargers. So, in a sense, Harris has already accomplished the near-impossible.